Mixing detector circuit arrangement



1952 A. Jfw. M. VAN OVERBEEK 17,022

MIXING. DETECTOR CIRCUIT ARRANGEMENT Filed Jan. 21, 1948 A.J.W. M.'VAN OVERBEEK INVENTOR AGENT Patented Nov. 4, 1952 UNITED STATES PATENT OFFICE MIXING DETECTOR CIRCUIT- ARRANGEMENT Application January 21, 1948, Serial No. 3,476 In the Netherlands January 24, 1947 beek, Eindhoven,

3 Claims.

The invention relates to a mixing detector circuit-arrangement for detecting frequencymodulated oscillations, in which the frequencymodulated oscillations required to be detected are fed to one of two interconnected circuits and in which the phase-displaced oscillations set up across the two circuits are fed to two controlgrids of a mixing tube. If the phase-displacement between the oscillations fed to the two controlgrids varies with the frequency of the oscillations supplied, the anode current of the mixing tube contains a low-frequency component which, to a first approximation, is proportional to the frequency sweep of the oscillations to be detected. A circuit-arrangement of this kind is described, for example, in the prior patent specification No. 660,875 (PH. 9272).

The coupled circuits, from which the two phase-displaced oscillations are taken must constitute a network which satisfies the following conditions:

1. The phase-displacement between the two output oscillations must be approximately 90 for the central frequency of the oscillations to be detected.

2. The phase-displacement must, even for the greatest frequency sweep, be proportional to the frequency sweep.

3. The proportionality factor between this phase-displacement and the frequency sweep must be a maximum.

4. The characteristic curve which illustrates the phase-displacement as a function of frequency must extend horizontally for frequency sweeps exceeding the highest frequency sweep occurring.

The first condition guarantees a symmetrical field of operation.

Fulfilment of the second condition ensures distortion-free detection, fulfilment of the third condition ensures high sensitiveness. The fourth condition has the effect of cutting 01f peaks in the transmitted signal. This condition excludes a receding characteristic curve corresponding to circuits not tuned to the central frequency, for great frequency sweeps; in this case peak voltages in the signal to be transmitted would lead to excessive distortions of the detected signal.

A circuit-arrangement comprising two coupled circuits satisfies the first, third and fourth of the aforesaid conditions but the linearity is insufiicient for great frequency sweeps.

The invention has for its object to provide a circuit-arrangement which while complying with all the above mentioned requirements is adapted to be carried out at a very low cost.

According to the invention, the second of the two coupled circuits has coupled to it a third circuit which is tuned to the central frequency of the oscillations to be detected. The coupling and the damping of this third circuit may be such that a more satisfactory straight-line relationship is ensured.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which the sole figure shows, by way of example, one embodiment.

In the mixing detector circuit-arrangement shown in the figure the oscillations to be detested are fed through a lead I to a network 2 which comprises the two coupled circuits 3 and 4 across which are produced two voltages which are fed to the two control-grids 5 and 6 of a mixing tube I. The circuit 4 is tuned to the central frequency of the oscillations to be detected, so that the phase difference between the voltage across the grid 5 and that across the grid 6 is for the central frequency. In this case the anode current of the tube 1 contains a lowfreqeuncy component which, to a first approximation, is proportional to the frequency sweep of the oscillations to be detected. For great frequency sweeps, however, the divergence from the straight-line relationship is inadmissibly large. For this purpose, according to the invention, provision is made of a circuit 8 which is coupled to the circuit 4 and which is also tuned to the central frequency of the oscillations to be detected.

It is found that the divergence from the straight-line relationship is least if the formula:

D32=a.K32+b is complied with, where is the quotient of the damping factors of the third circuit and the second circuit:

What I claim is:

1. A mixing detector circuit arrangement for a signal voltage having frequency deviations about a given central frequency, comprising an electron discharge tube having in the order named a cathode, first and second control grids and an anode, a first resonant circuit tuned to said given central frequency, a second resonant circuit tuned to said given central frequency and coupled to said first resonant circuit, means to apply said signals to said first resonant circuit, means to derive a first voltage from said first resonant circuit and to apply said first voltage to one of said control grids, means to derive a second voltage in phase quadrature with said first voltage at said given central frequency from said second resonant circuit and to apply said second voltage to the other of said control grids thereby to vary the anode current of said tube proportional to the frequency deviations of said signals, and a third resonant circuit tuned to. said given central frequency and inductively coupled solely to said second resonant circuit thereby to linearize the relationship between said anode current variation and the frequency deviations of said signal voltage.

2. A mixing detector circuit arrangement for a signal voltage having frequency deviations about a given central frequency, comprising an electron discharge tube having in the order named a cathode, first and second control grids and an anode, a first parallel resonant circuit tuned to said given central frequency, a second parallel resonant circuit tuned to said given central frequency and inductively coupled to said first resonant circuit, means to apply said signals to said first resonant circuit, means to derive a first voltage from said first resonant circuit and to apply said first voltage to one of said control grids, means to derive a second voltage in phase quadrature with said first voltage at said given central frequency from said second resonant circuit and to apply said second voltage to the other of said control grids thereby to vary the anode current of said tube proportional to the frequency deviations of said signals, and a third parallel resonant circuit tuned to said given central frequency and inductively coupled solely to said second parallel resonant circuit thereby to linearize the relationship between said anode current variation and the frequency deviations of said signals.

3. A mixing detector circuit arrangement for a signal voltage having frequency deviations 4 about a given central frequency, comprising an electron discharge tube having in the order named a cathode, first and second control grids and an anode, a first resonant circuit tuned to said given central frequency, a second resonant circuit having a given damping factor and being tuned to said given central frequency and coupled to said first resonant circuit, means to apply said, signals to said first resonant circuit, means to derive a first voltage from said first resonant circuit and to apply said first voltage to one of said control grids, means to derive a second voltage in phase quadrature with said first voltage at said given central frequency from said second resonant circuit and to apply said second voltage to the other of said control grids thereby to vary the anode current of said tube proportional to the frequency deviations of said signals, and a third resonant circuit having a second given damping factor and being tuned to said given central frequency and inductively coupled with a given coupling solely to said second resonant circuit thereby to linearize the relationship between said anode current variation and the frequency deviations of said signals, said given coupling between said second and third resonant circuits and said given damping factors of said second and third resonant circuits satisfying the relationship:

D32:aK';2+b

where D32 represents the quotient of the damping factors of the third resonant circuit and the second resonant circuit, a is a first constant having a value between 1.5 and 2.5, K32 represents the quotient of the given coupling between said third resonant circuit and said second resonant circuit multiplied by said given central frequency and the loss resistance of said second resonant circuit, and b is a second constant having a value between 0.2 and 0.3.

ADRIANUS JOHANNES WILHELMUS MARIE VAN OVERBEEK.

REFERENiJES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,343,263 Okrent Mar. 7, 1944 2,445,996 Bradley July 27, 1948 2,448,177 Gavin Aug. 31, 1948 2,448,908 Parker Sept. 7, 1948 2,457,016 Vilkomerson Dec. 21, 1948 

